The present invention relates to air-conditioning equipment for a vehicle and more particularly to air-conditioning equipment provided with an improved drive unit for driving the actuators.
Conventionally, air-conditioning equipment for a vehicle, such as shown in FIG. 10 and disclosed by Japanese Patent Kokai No. 58-209609, consists of an outside air/inside air changing shutter 2 mounted in a duct 1, a blower 3, an evaporator 4, an air mixing shutter 5, a heater 6, a mode selecting shutter 7, a defrost side outlet 9, a face side outlet 8, and a foot side outlet 10. The evaporator 4 consititutes a cooling system together with a compressor 11, a condensor 12, a receiver tank 13, and an expansion valve 14. The rotation of an engine 15 is transmitted to the compressor 11 through a magnet clutch 16.
An A/D converter 17 converts respective analog signals of the inside temperature Tr sensed by an inside air sensor 18 mounted inside the vehicle compartment, the opening .theta. of the air mixing shutter 5 detected by a position detecting potentionmeter 19, the sunlight temperature Ts detected by a sunlight sensor 20, the outside or ambient temperature Ta detected by an outside temperature sensor 21, the duct temperature Tm detected by a mode sensor 22 mounted in the duct 1, the set or desired temperature Td supplied from a temperature setting unit 23, and the water temperature Tw supplied from a water temperature switch 90 into the corresponding digital signals and feeds these resultant digital signals to a control unit 24.
The control unit 24 consists of a microcomputer which includes a changing shutter controlling section 27 for controlling the outside air/inside air changing shutter 2 through a switching circuit 25 and an actuator 26, a compressor controlling section 29 for controlling the magnet clutch 16 through drive circuit 28, a blower controlling section 31 for controlling the blower 3 through a drive circuit 65, an air mixing shutter controlling section 34 for controlling the air mixing shutter 5 through a drive circuit 60 and an actuator 50, a mode selecting shutter controlling section 37 for controlling the mode selector shutter 7 through a switching circuit 35 and an actuator 36, and an arithmetic and logical unit 38 which performs arithmetic operations on each of the temperatures Tr, Ts, Ta, Tm, and Td, and sends out the results to the respective controlling sections 27, 29, 31, 34, and 37. A manual switch 39 is provided for manually controlling the blower 3.
The compressor controlling section 29 is provided for keeping the temperature of the evaporator 4 constant by turning the compressor 11 off when the duct temperature Tm goes down to a lower limit (stored in a setting unit 41) that is somewhat higher than the temperature at which the evaporator 4 is frozen and on when the duct temperature Tm goes up to an upper limit (stored in a setting unit 40) that is higher than the above freezing point by the gap of a hysteresis curve. As described above, the arithmetic and logic unit 38 performs arithmetic operations on each of the temperatures Tr, Ts, Ta, Tm, and Td and sends out the resultant signal or heat load signal to the changing shutter controlling section 27, the compressor controlling section 29, the blower controlling section 31, the air mixing shutter controlling section 34, and the mode selecting shutter controlling section 37. Each of the above control sections controls the changing circuit 25 or 35, or the drive circuits 28, 65 or 60.
The respective actuators 26, 50, and 36 are driven to control the changing shutter 2, the air mixing shutter 5, and the mode selecting shutter 7 in accordance with the characteristics shown in FIGS. 11(a), 11(b), 11(c), and 11(d), while the blower 3 and the compressor 11 are controlled in accordance with the characteristic curve shown in FIG. 11(e).
The heat load signal F is given by the following formula: EQU F=(A.Tr+B.Ts+C.Tm)-Td
wherein A, B and C are constants.
When the heat load signal F decreases to a certain point along the characteristic line shown in FIG. 11(a), the changing shutter 2 is turned from the outside air intake mode to the inside air intake mode as shown in FIG. 11(b). As the heat load signal F decreases, the opening .theta. of the air mixing shutter 5 also decreases as shown in FIG. 11(c) to increase the mixing ratio of cool air. The mode selecting shutter 7 is switched from the foot side output mode to the face side output mode through the bi-level mode as shown in FIG. 11(d). As the heat load signal F decreases, the blower speed first decreases toward a low speed limit, stays at the low speed level for a while and then increases toward a high speed limit as shown in FIG. 11(e).
The control unit or microcomputer 24 incorporates various controlling devices, such as the changing shutter controlling section 27, the air mixing shutter controlling section 34, the mode selecting shutter controlling section 37, so that it is complicated and expensive to construct. In addition, it is troublesome and expensive to replace any of the actuators 26, 36, and 50, with another actuator of a different capacity or type because the control unit itself must be replaced. Moreover, there is a danger that all the actuators stop working when the central control unit 24 becomes out of order.